This disclosure relates to a weld gun for resistance welding metal components, such as fasteners, to a metallic object, such as sheet metal. More particularly, this disclosure relates an electrode assembly for indirect sensing of fastener position.
Weld gun assemblies are used to resistance weld fasteners to metallic objects such as body panels for vehicles. A fastener, such as a weld stud or nut, is loaded onto one of the electrodes. The electrodes are moved together with an actuator thereby placing the fastener into engagement with the panel under pressure. Very high currents are applied to the electrodes, which welds the fastener to the panel.
The use of weld guns is typically an automated process in which the fasteners are loaded into the weld gun assembly. Occasionally, the fastener is not properly loaded into the weld gun or the fastener may not be loaded into the weld gun at all. Under these circumstances, it is important to detect that there is a problem with the fastener so that the fastener can be properly welded to the panel. To this end, sensors have been used in an effort to determine the presence and orientation of the fastener in the weld gun. Typically, a linear variable displacement transducer (LVDT) has been connected to an electrode arm to measure the movement of the arm. If no nut is present, then the arm will move a greater amount than if a fastener is present and in the proper orientation. If the fastener is not in the proper orientation, then the electrode arm will move slightly less than if the fastener is in the proper orientation. In this manner, fastener presence and orientation has been detected. However, it has been difficult to accurately detect the proper orientation of the fastener for several reasons.